How to Make a Hypertufa Planter for Your Garden
Although it sounds like a space-aged soy product, hypertufa is a mixture consisting of cement, peat moss, and perlite. All of these materials are readily available at any home or garden center. The name comes from tufa, a natural porous rock that looks like a weathered pumice stone. English farmers would carve troughs out of the soft stone for use on their farms for feeding or watering their livestock to planting.
All you have to do is combine the ingredients, add water, pack the mixture into a mold, and set it aside to cure for a couple of days. When you pop off the mold you will have a realistic and long-lasting planter for your own garden or patio. These troughs will last for years and will look better with age.
Building a Form
The forms can be made from plywood, rigid foam insulation, or two plastic storage boxes, one inside the other. You can also use round storage bins of two different sizes. Another method is using a terra cotta bowl or pot inverted onto a piece of plywood and packing the hypertufa around the pot.
If you plan on making several planters, using pine boards would be a good option as it will last longer. You can also add decorative recesses by gluing beveled panels to the insides of the exterior form. Since this is a form you should not have very intricate details on the accents and the edges should be beveled or eased to allow the mold to be easily removed.
For best results, the walls should be a minimum of 2 1/2 inches thick, and the planter should be at least 7 inches deep.
Use screws to construct two wooden boxes so that you can remove the sides easily when unmolding. Screw the inner box form from the inside so you can remove the screws and release the inner mold.
Foam board mold
The amount of hypertufa mix you will need depends on the size of the planter you're making. You can increase or decrease the recipe if you stick to these basic proportions:?
3 parts cement
4 parts peat
4 parts perlite
Water sufficient to make a firm, moldable mixture, plus liquid acrylic (about ¼ the amount of total liquid)
A handful of nylon reinforcing fibers – available at home centers.
Wire mesh or fiberglass mesh – optional
PVC pipe – 1 ½ diameter
Masonry drill bit and drill – if adding drainage holes afterwards
1. Paint on a release agent
The wood must first be coated with a release agent to prevent the hypertufa from adhering to the form. You can use a piece of plastic sheeting or spray the inside of wooden forms with a waterproofing sealant. Melted paraffin wax works well, but you must work quickly and wear rubber gloves to prevent any accidental burns. The wax can be removed later with a wire brush.
2. Drainage holes
To ensure proper drainage, you'll need to create holes in the bottom of the planter. You can space four 2½-inch-tall pieces of PVC pipe (or whatever the thickness of the bottom of the planter is) secured with some hot glue or plumber’s putty to the outer form. You can also drill out drainage holes after the planter has cured with a ¾ inch masonry bit. You will need more holes since the diameter is smaller.
3. Mix ingredients
While wearing gloves, dust mask, and goggles, mix the cement, peat moss, and perlite in a large tub or cement planter. Add the water and acrylic additive a few cups at a time until the mix sticks together but is not runny. Add nylon reinforcing fibers and add them to the mix. You should be able to form the fiber-reinforced mix into a solid ball that doesn't fall apart.
4. Filling the form
When packing the hypertufa mix into the form, take care not to knock the drainage pipes out of place. Pack the mix tightly, starting with the bottom. When you've packed the bottom to a thickness of at least 2½ inches, insert the inner form and begin packing tightly up the sides. Place the mixture in between the forms with a garden or mason’s trowel. Remember, the tighter you pack, the stronger your planter will be. Some people like to add wire mesh to help reinforce the planter, but this should be done only if you are making a very large or very thick planter. Cut the mesh to size for the bottom and four sides and center it between the forms while adding the hypertufa mix.
As you pack the hypertufa mixture up the sides, tamp it down with a flat piece of wood or dowel to get rid of any air pockets. Continue adding and tamping until the mixture is flush with the top of the outer box. A loose pack will show up as a “honeycomb” structure when the forms are removed.
6. Remove planter from form
The planter will need at least 24 hours to cure before you can remove the mold. It is cured when you can't scratch the surface with a fingernail. Remove all the screws and take off the bottom panel. Then remove the outside walls, popping the boards free of the paraffin with a flat trowel or putty knife. Push the walls of the inside form toward the center so they collapse inward on themselves.
When first unmolded, the planter is soft enough to be textured by going over the surface with a coarse wire brush and removing any sharp corners. Once finished, wrap it in plastic and leave it in a cool place to cure for about 28 days to reach maximum strength. This is a property of cement not of hypertufa.
You can place almost any type of plant in the planter. Traditionally, they're used for rugged alpine plants, which thrive in the porous containers. Small and slow-growing, yet with beautiful flowers, alpines are well-suited for the limited confines of a planter garden. Good choices are herbaceous perennials and dwarf shrubs and conifers. Keep scale in mind.
The best planting mixture for alpines is organic soil with sand and small stones. A layer of gravel at the bottom of the planter will aid drainage. Before filling the planter, put a small piece of wire mesh over each drainage hole to keep it clear.
If you leave the planter outside in the winter keep it planter shaded to limit repeated freeze-thaw cycles that can harm plants and also shorten the life of the planter.